Push-on type retaining fasteners are well known in the prior art. Such fasteners are commonly made in one piece for example by stamping thin wall resilient metal such as sheet metal to provide what is characteristically a frusto-conical shaped washer in appearance.
Such fasteners have historically featured a hollow frusto-conical projection having generally axial aligned entrance and exit openings that are both circular with the exit opening surrounded by an edge of the fastener adapted such that, when a cylindrical member is received through the entrance opening by pushing the fastener in a direction thereagainst, the edge provides a continuous circumferential engagement therewith that is operative to frictionally secure the fastener to the member when one attempts to remove the fastener in an opposite direction.
Examples of prior art fasteners of the type of interest to the present invention may be seen by reference to U.S. Pat. Nos. 2,975,667; 2,986,060; 3,032,807; 3,108,371; and 4,385,431, the disclosures of which are included herein by reference. Generally, such fasteners feature a circular exit aperture circumscribed by a retaining edge that is unable to stretch and is thus limited to cylindrical members having small diameter variations or which in some cases feature circumferentially spaced slits extending radially outwardly through the projection wall to provide a plurality of resilient arms that, although can expand to accommodate a broader range of cylindrical diameters, may tend to split along the slit or promote flex fatigue due to the reduced circumferential breadth of the individual arms.
An example of a push-on type fastener having a non-circular exit opening is disclosed in FIGS. 1-3 of U.S. Pat. No. 1,675,277, the disclosure of which is incorporated herein by reference. However, the intersections of the adjacent arcuate edges forming the non-circular opening is shaped into sharp projections which extend radially inwardly and are highly susceptible to breakage.
An example of a fastener for a door handle having what at first appears to be a non-circular opening but actually is not by comprising a plurality of opposed arcuate spaced teeth for engaging a part of the handle that are arranged in a circular configuration is disclosed in U.S. Pat. No. 1,808,048, the disclosure of which is incorporated herein by reference.
Finally, an example of a retainer having a generally square shaped opening adapted to enable a generally square shaped portion of a shaft to extend therethrough is disclosed in U.S. Pat. No. 3,419,292, the disclosure of which is incorporated herein by reference.
Thus, prior art push-on type fasteners have historically featured either circular or non-circular apertures surrounded either by a smooth retaining edge operative to secure a cylindrical shank having only small diameter variations or in many cases by spaced projecting teeth subject to breakage or that include radial slots and the like subject to splitting.
The shortcomings of prior art fasteners are overcome by the fastener of the present invention by the discovery that changing the exit aperture to a non-circular aperture defined between at least two spaced-apart retaining edges that enable the fastener to accommodate a broad range of cylindrical diameters as well as including means enabling the retaining edges to stretch to prevent their splitting as the diameter increases from a minimum to a maximum.